1. Field of the Invention
The present invention relates to an adaptive array antenna receiving apparatus.
2. Description of the Related Art
FIG. 13 is a block diagram showing a conventional adaptive array antenna receiving apparatus. The adaptive array antenna receiving apparatus receives carrier frequency signals from antennas a, b, and c. Then, receiving RF sections 1301, 1302, and 1303 down convert these carrier frequency signals to intermediate frequency signals, thereafter demodulate into base band signals which are in-phase component (I-ch), and an orthogonal component(Q-ch), respectively. A/D converters 1304 to 1309 convert the base band signals to digital signals, respectively.
Complex multiplying circuits 1310,1311, and 1312 carry out a complex multiplication of outputs signals of the A/D converters 1304 to 1309 in accordance with an output of a weighting factor controlling circuit 1313, respectively and the multiplication results are added by an adding circuit 1314. Thus the adaptive array antenna reception is carried out by above procedure. Then, a decoding circuit 1315 decodes the received signal.
The weighting factor of the weighting factor controlling circuit 1313 is updated using a unique word when a synchronous burst is received. At a unique word receiving interval, a switch SWa 1316 is closed and the signals digitized by the A/D converters 1304 to 1309 are transferred to the weighting factor controlling circuit 1313.
Resultant signals received by the adaptive array antenna, serving as added outputs, are transferred to a differential circuit 1318 when a switch SWb 1317 is closed. The unique word for synchronous burst is transferred to a modulating circuit 1320 when a switch SWc 1319 is closed.
The modulating circuit 1320 modulates a unique word pattern of the synchronous burst. The differential circuit 1318 subtracts a signal, which is obtained by modulating the unique word pattern, from the resultant signals received by the adaptive array antenna, thereby calculating an error between these signals.
The weighting factor controlling circuit 1313 calculates a new weighting factor based on the error signal, the received signal from each antenna, and the weighting factor previously sampled, updating the weighting factor of the weighting factor controlling circuit 1313.
In the adaptive array antenna receiving apparatus of this figure, the switch SWc 1319 is connected to the unique word side at the unique word receiving interval, and connected to a decoding result of a message at a message-receiving interval. By such an operation, this receiving apparatus updates the weighting factor using both the unique word and message intervals.
In order to obtain more proper the weighting factor, there is a decision feedback typed adaptive array antenna receiving apparatus which feeds back the output of the decoder shown in FIG. 13 to the modulator.
FIG. 14 is a block diagram showing such a conventional decision feedback typed adaptive array antenna receiving apparatus. In this decision feedback typed adaptive array antenna receiving apparatus of this figure, a switch SWc 1419 is connected to the unique word side at the unique word receiving interval, and connected to the decoding result of the message at the message-receiving interval. By such an operation, the receiving apparatus updates the weighting factor using both the unique word and message intervals.
In this apparatus, a known symbol sequence such as a unique word is used as a reference signal, thereby updating the weighting factor, while the decision feedback of a decode signal Sfb of a message is performed and the signal is used as a reference signal, updating the weighting factor.
In a normal case, since the message portion is not the known symbol sequence, such a portion is not used as a reference signal. However, in a case that an error rate of the message portion is about 10.sup.-2, the number of errors in one slot is small. As a result, the decided symbol is regarded as substantially a correct symbol, and the signal of the message portion is used as a reference symbol.
Thus, in the conventional decision feedback typed adaptive array antenna receiving apparatus, the weighting factor of the weighting factor controlling circuit 1313 was updated by use of the unique word, thereafter the weighting factor was updated by use of the message portion as an auxiliary way.
In these conventional adaptive array antenna receiving systems, however, a discrimination between a desired station and an interference station cannot be made when the unique word of the desired station and that of the interference station are the same. As a result, a wave directivity, which should be directed to the desired station as shown in FIG. 15, will be directed to both the desired station and the interference station as shown in FIG. 16. In other words, the adaptive array antenna has the technique in which the desired station and the interference station are separated by directivity. However, in the above case, the unique word cannot be correctly received from the desired station because of the interference caused by receiving the waves of the desired station and the interference station simultaneously.
An object of the present invention is to provide an adaptive array antenna receiving apparatus, which can extract a signal of a desired station from receiving signals even if there is an interference station having the same known signal pattern as that of the desired station.